Extensible markup language (XML) is increasingly becoming the preferred format for transferring data. XML is a tag-based hierarchical language that provides the ability to represent data in diverse formats and contexts. For example, XML can be used to represent data spanning the spectrum from semi-structured data (such as one would find in a word-processing document) to generally structured data. XML is well-suited for many types of communication including business-to-business and client-to-server communication.
Data represented in XML is often created and retained in electronic documents, such as electronic forms. The structure of an electronic form that is written in XML typically is governed by an XML schema (XSD) and this structure can be altered by applying an eXtensible Style-sheet Language Transformation (XSLT) file on the form. For more information on XML, XSLT, and XSD (schemas), the reader is referred to the following documents which are the work of, and available from the W3C (World Wide Web consortium): XML Schema Part 2: Datatypes; XML Schema Part 1: Structures; and XSL Transformations (XSLT) Version 1.0; and XML 1.0 Second Edition Specification.
Databases are computerized information storage and retrieval systems. A Relational Database Management System (RDBMS) is a database management system (DBMS) which uses relational techniques for storing and retrieving data. RDBMS software using a Structured Query Language (SQL) interface is well known in the art. The SQL interface has evolved into a standard language for RDBMS software and has been adopted as such by both the American National Standards Organization (ANSI) and the International Standards Organization (ISO). The information stored in a RDBMS is typically hierarchical in nature. Parent-child relationships are defined through integrity constraints across multiple relational tables. But it frequently makes sense to present this information to humans (or other applications) as hierarchical information, which can be done using XML.
When hierarchical database information is persisted as a structured XML document, a unique set of challenges are created in translating the changes to the XML document back into the database. For example, while XML data is by nature hierarchical, typically the only relationship between a parent and a child is the fact that the child is contained within the parent. By contrast, in a database both parent and child will contain common data kept in sync through referential integrity.
When XML is used as a temporary persistence format for data retrieved from a hierarchical database to be consumed by a wide variety of applications (e.g., web services, internet application, thin client applications), it is important that the retrieved information can be returned to its original storage format (e.g., a database) properly reflecting the changes made by the application(s) that manipulated the data.